Who introduced the three-domain system of classification? Explain its main features.

(N/A) The three-domain system of classification was proposed by $Carl$ $Woese$.
$\Rightarrow$ In this system,the kingdom $Monera$ is divided into two domains,while all eukaryotic kingdoms are placed in the third domain,eventually leading to the six-kingdom classification.
$\Rightarrow$ In earlier classification systems,$Bacteria$,$Blue-Green$ $Algae$,$Fungi$,$Mosses$,$Bryophytes$,$Pteridophytes$,$Gymnosperms$,and $Angiosperms$ were all grouped under 'Plants'.
$\Rightarrow$ The common feature for all these was the presence of a cell wall in their cells.
$\Rightarrow$ However,organisms grouped together in this system differed widely in other characteristics. For example,$Prokaryotic$ $Bacteria$ and $Blue-Green$ $Algae$ were grouped with $Eukaryotic$ organisms.
$\Rightarrow$ Furthermore,unicellular $Chlamydomonas$ and multicellular $Spirogyra$ were placed together under 'Algae'.
$\Rightarrow$ The system did not differentiate between heterotrophic $Fungi$ and autotrophic plants,despite differences in cell wall composition (e.g.,$Fungi$ have $Chitin$ in their cell walls,while plants have $Cellulose$).
$\Rightarrow$ When these differences were considered,$Fungi$ were placed in a separate kingdom,$Fungi$.
$\Rightarrow$ All $Prokaryotic$ organisms were grouped under kingdom $Monera$,and all unicellular $Eukaryotic$ organisms were placed in kingdom $Protista$.
$\Rightarrow$ Consequently,$Chlorella$ and $Chlamydomonas$ (which have cell walls) and $Amoeba$ and $Paramecium$ (which lack cell walls) were placed together in kingdom $Protista$.
$\Rightarrow$ Modern classification systems focus not only on morphological,physiological,and reproductive similarities but are also based on $Phylogenetic$ (evolutionary) relationships.